1. Field of the Invention
The present invention relates to an ink jet print head for expelling ink from a number of nozzles to a print sheet for printing and a method for producing the same. More specifically, this invention relates to an ink jet print head in which a driving electrode of an actuator corresponding to each of nozzles is directly connected to wiring of a driver circuit formed on a substrate, and a method for producing the same.
2. Description of Related Art
Commonly, in ink jet print heads of an on-demand system used for an ink jet printer, the print head is a piezo system in which a piezoelectric element is used for the actuator. This print head has advantages in that the type of ink used is less limited since heat is not generated and its durability is excellent, as compared with a bubble jet print head in which a heat generating element is used for the actuator. The integration and miniaturization, which have been considered to be a weak point in the conventional piezo type, are improved by making use of a modification of a shear mode of the piezoelectric element, as disclosed, for example, in U.S. Pat. No. 5,016,028 (JP-A-2-150355). In recently designed ink jet print heads, considerable integration and miniaturization have been achieved.
The schematic construction of the conventional ink jet print head of this kind will be explained with reference to the drawings while referring also to a method for the production thereof. As shown in FIG. 10, which is an exploded perspective view, the print head comprises a ceramic plate 102 formed from a piezoelectric element, a cover plate 103 for covering the top thereof, a nozzle plate 131 formed with nozzles 132 from which ink is expelled, and a substrate 141 adhered to the lower surface of the ceramic plate 102.
The ceramic plate 102 is a plate made of ferroelectric ceramic material such as lead zirconate titanate (PZT) formed with a number of parallel channels 108. Each channel 108 is provided with a deep channel portion 117 and a shallow channel portion 116, between which is disposed an curved transition R portion 119. This channel 108 is preferably formed by a diamond cutter blade. The ceramic plate 102 is applied with polarization processing in a direction of the arrow P. Thereby, a side wall 111 between the channels 108 is polarized in that direction. Each channel 108 is formed at a depthwise upper half of the side thereof with an electrode 113, which is preferably a metal vapor-deposition film. The electrode 113 also covers the bottom surface of the shallow channel portion 116. The electrode 113 is formed by inclining the ceramic plate 102 at a suitable angle relative to a vapor deposition source and applying the vapor deposition twice from both sides.
For the cover plate 103, a ceramic or resin material is used, which is formed with an ink inlet 121 and a manifold 122. These are formed by grinding or cutting processing. The cover plate 103 is assembled by bonding the surface formed with the manifold 122 to the surface formed with the channel 108 of the ceramic plate 102 with an adhesive.
The nozzle plate 131 is a preferably plastic plate assembled by adhering the ends of the ceramic plate 102 and the cover plate 103. A nozzle 132 is provided at a position corresponding to each of the channels 108. The substrate 141 is formed with conductive pattern 142 at positions corresponding to each of the channels 108, with each conductive pattern 142 being connected to an electrode 113 of a channel 108 (the bottom portion of the shallow channel portion 116) by a conductor 143. This connection is done by wire bonding. Alternatively, this connection is sometimes made using a flexible substrate (FPC substrate) in place of the wire bonding. In this case, the electrode 113 is drawn to the plane portion from the shallow channel portion 116, with which an electrode pattern of the FPC substrate is registered, and they are joined by solder.
In the assembled print head, as shown in FIG. 11 which is a sectional view, the upper surfaces of the channels 108 are closed by the cover plate 103 to form a plurality of ink chambers 112. Ink is supplied to and filled in the ink chambers 112 via the ink inlet 121 and the manifold 122 of the cover plate 103.
In the thus configured print head, a positive driving voltage is applied to an electrode 113B of a specific ink chamber 112B by a driver circuit provided externally. When electrodes 113A and 113C of ink chambers 112A and 112C are grounded, electric fields reversed to each other are generated in side walls 111A and 111B to deform the ink chamber 112B so as to reduce the volume thereof, as shown in FIG. 12. Thus, ink is jetted out of the nozzles 132 in communication with the ink chamber 112B of the nozzle plate 131 for printing. When the application of the driving voltage stops, the side walls 111A and 111B return to the FIG. 11 state, and the ink chamber 112B is replenished with ink via the ink inlet 121 and the manifold 122.
However, the conventional ink jet print head and method for producing the same as described above have the problem described below. That is, since the contact between the electrodes 113 of the channels 108 and the driver circuit is made by the wire bonding through the conductive pattern 142 of the substrate 141, the same number of bonding elements as that of the channels 108 is necessary. Further, the channel 108 must have a complicated shape including the shallow channel portion 116 because ink cannot be allowed to pass through the conductor 143, which must be sealed. Accordingly, not only the fabrication step for the wire bonding and the processing step for formation of channels are complicated, but also the cost required therefor greatly increases as the high integration progresses.
Further, since the control of the electrodes 113 must be done via each conductor 143 subjected to the wire bonding, a driver circuit formed into a matrix cannot be used. Because of this, a number of individual diodes are used to assemble the driver circuit, which requires very many parts, thus impeding the provision of a high integration.
Even in the case where the FPC substrate is used in place of the wire bonding, it is necessary to make the pitch of the electrode pattern of the FPC substrate narrow to correspond to the channels 108 of the ceramic plate 102, similarly posing a problem of cost. Even in the case where wire bonding and FPC substrate are used, the cost for high integration increases, thus impeding the improvement in resolution of the print head.